The grantor, by a provision in the grant, may during his lifetime elect, in relation to the property conveyed and to the erection, maintenance, and management of the hospital, to perform all the duties and exercise all the powers which, by the terms of the grant, are enjoined upon and vested in the trustee. In such case the powers and duties conferred and imposed by the grant upon the trustee shall be exercised and performed by the grantor during his lifetime. Upon the death of the grantor the powers and duties shall devolve upon and be exercised by the trustee or his successor.